Various sampling systems have been developed in the art to collect signatures of interest from air, water and other ambient fluids. Such systems are utilized, for example, to detect the emission of environmental pollutants at industrial sites, as part of environmental remediation efforts, or in the enforcement of chemical or nuclear arms treaties. Typically, such systems are designed to capture signatures of interest on a medium that is absorbent or attractive to signatures of interest. The captured signatures may later be desorbed, typically by heating the medium or through chemical extraction. The desorbed signatures may then be subjected to chemical, biological or radiological analysis. In the case of chemical signatures, for example, gas chromatography/mass spectrometry (GC/MS) is frequently utilized to analyze the signatures.
Alternatively, in some applications, the captured signatures may be caused to undergo a reaction to make a new signature that is more useful. For example, in some applications, formaldehyde and other aldehydes are reacted with 2,4-Dinitrophenylhydrazine (DNPH) to form stable hydrazones, which may be extracted from the silica gel and analyzed by liquid chromatography.
Sampling systems of the foregoing type may be active or passive. In active sampling systems, the fluid of interest (which may be, for example, ambient air or water) is actively pumped or drawn into or through the sampling media. By contrast, passive sampling systems typically rely on passive mechanisms for signature capture, such as the unassisted molecular diffusion of gaseous analytes through a diffusive surface onto an adsorbent medium. In many implementations, the sampling media is disposed in a stainless steel or glass tube equipped with an inlet and an outlet.
Various media may be utilized in the foregoing sampling systems. Generally, it is desirable for the sampling media to (a) provide an acceptable pressure drop during sampling, (b) exhibit sufficient capacity or breakthrough volume for the application to which the media is directed, (c) be suitably absorbent or attractive to signatures of interest under typical sampling conditions, (d) be capable of desorbing these signatures or otherwise permitting their analysis under suitable laboratory conditions, and (e) in the case of chemical signatures, to not interfere with the chemical fingerprint of the signatures in GS/MS or other commonly used analytical methods. Graphitized carbon black (GCB) of varying particle sizes is commonly used as a sampling media in sampling devices intended for use with organic chemical signatures, due to its affinity for common organic chemicals under sampling conditions and its ability to readily undergo thermal desorption of these materials. In a typical implementation, the GCB is disposed as a packed bed within a glass or stainless steel tube equipped with an inlet and an outlet.